#!/usr/bin/env python3
import matplotlib.pyplot as plt
filename = 'a.txt'
X,Y = [],[]
with open(filename, 'r') as f:#1
    lines = f.readlines()#2
    for line in lines:#3
        value = [float(s) for s in line.split()]  #4
        X.append(value[1])#5
        Y.append(value[2])

plt.plot(X, Y)
plt.show()
